NKCC1 controls GABAergic signaling and neuroblast migration in the postnatal forebrain

Genetically encoded sensors for Chloride concentration

Insights into chloride regulation in neurons have come slowly, but they are likely to be critical for our understanding of how the brain works. The reason is that the intracellular Cl^- level ([Cl^-]_i) is the key determinant of synaptic inhibitory function, and this in turn dictates all manner of neuronal network function. The true impact on the network will only be apparent, however, if Cl^- is measured at many locations at once (multiple neurons, and also across the subcellular compartments of single neurons), which realistically, can only be achieved using imaging. The development of genetically-encoded anion biosensors (GABs) brings the additional benefit that Cl^- imaging may be done in identified cell-classes and hopefully in subcellular compartments. Here, we describe the historical background and motivation behind the development of these sensors and how they have been used so far. There are, however, still major limitations for their use, the most important being the fact that all GABs are sensitive to both pH and Cl^-. Disambiguating the two signals has proved a major challenge, but there are potential solutions; notable among these is ClopHensor, which has now been developed for in vivo measurements of both ion species. We also speculate on how these biosensors may yet be improved, and how this could advance our understanding of Cl^- regulation and its impact on brain function.

Altered Cl- homeostasis hinders forebrain GABAergic interneuron migration in a mouse model of intellectual disability

Impairments of inhibitory circuits are at the basis of most, if not all, cognitive deficits. The impact of OPHN1, a gene associate with intellectual disability (ID), on inhibitory neurons remains elusive. We addressed this issue by analyzing the postnatal migration of inhibitory interneurons derived from the subventricular zone in a validated mouse model of ID (OPHN1^-/y mice). We found that the speed and directionality of migrating neuroblasts were deeply perturbed in OPHN1^-/y mice. The significant reduction in speed was due to altered chloride (Cl^-) homeostasis, while the overactivation of the OPHN1 downstream signaling pathway, RhoA kinase (ROCK), caused abnormalities in the directionality of the neuroblast progression in mutants. Blocking the cation-Cl^- cotransporter KCC2 almost completely rescued the migration speed while proper directionality was restored upon ROCK inhibition. Our data unveil a strong impact of OPHN1 on GABAergic inhibitory interneurons and identify putative targets for successful therapeutic approaches.

Nerves in the Tumor Microenvironment: Origin and Effects

Studies have reported the vital role of nerves in tumorigenesis and cancer progression. Nerves infiltrate the tumor microenvironment thereby enhancing cancer growth and metastasis. Perineural invasion, a process by which cancer cells invade the surrounding nerves, provides an alternative route for metastasis and generation of tumor-related pain. Moreover, central and sympathetic nervous system dysfunctions and psychological stress-induced hormone network disorders may influence the malignant progression of cancer through multiple mechanisms. This reciprocal interaction between nerves and cancer cells provides novel insights into the cellular and molecular bases of tumorigenesis. In addition, they point to the potential utility of anti-neurogenic therapies. This review describes the evolving cross-talk between nerves and cancer cells, thus uncovers potential therapeutic targets for cancer.

NKCC1, an Elusive Molecular Target in Brain Development: Making Sense of the Existing Data

Ionotropic GABA transmission is mediated by anion (mainly Cl⁻)-permeable GABA_A receptors (GABA_ARs). In immature neurons, GABA exerts depolarizing and sometimes functionally excitatory actions, based on active uptake of Cl⁻ by the Na-K-2Cl cotransporter NKCC1. While functional evidence firmly shows NKCC1-mediated ion transport in immature and diseased neurons, molecular detection of NKCC1 in the brain has turned out to be extremely difficult. In this review, we describe the highly inconsistent data that are available on the cell type-specific expression patterns of the NKCC1 mRNA and protein in the CNS. We discuss the major technical caveats, including a lack of knock-out-controlled immunohistochemistry in the forebrain, possible effects of alternative splicing on the binding of antibodies and RNA probes, and the wide expression of NKCC1 in different cell types, which make whole-tissue analyses of NKCC1 useless for studying its neuronal expression. We also review novel single-cell RNAseq data showing that most of the NKCC1 in the adult CNS may, in fact, be expressed in non-neuronal cells, especially in glia. As future directions, we suggest single-cell NKCC1 mRNA and protein analyses and the use of genetically tagged endogenous proteins or systematically designed novel antibodies, together with proper knock-out controls, for the visualization of endogenous NKCC1 in distinct brain cell types and their subcellular compartments.

Excitation/inhibition imbalance and impaired neurogenesis in neurodevelopmental and neurodegenerative disorders

The excitation/inhibition (E/I) balance controls the synaptic inputs to prevent the inappropriate responses of neurons to input strength, and is required to restore the initial pattern of network activity. Various neurotransmitters affect synaptic plasticity within neural networks via the modulation of neuronal E/I balance in the developing and adult brain. Less is known about the role of E/I balance in the control of the development of the neural stem and progenitor cells in the course of neurogenesis and gliogenesis. Recent findings suggest that neural stem and progenitor cells appear to be the target for the action of GABA within the neurogenic or oligovascular niches. The same might be true for the role of neuropeptides (i.e. oxytocin) in neurogenic niches. This review covers current understanding of the role of E/I balance in the regulation of neuroplasticity associated with social behavior in normal brain, and in neurodevelopmental and neurodegenerative diseases. Further studies are required to decipher the GABA-mediated regulation of postnatal neurogenesis and synaptic integration of newly-born neurons as a potential target for the treatment of brain diseases.

Overlapping migratory mechanisms between neural progenitor cells and brain tumor stem cells

Neural stem cells present in the subventricular zone (SVZ), the largest neurogenic niche of the mammalian brain, are able to self-renew as well as generate neural progenitor cells (NPCs). NPCs are highly migratory and traverse the rostral migratory stream (RMS) to the olfactory bulb, where they terminally differentiate into mature interneurons. NPCs from the SVZ are some of the few cells in the CNS that migrate long distances during adulthood. The migratory process of NPCs is highly regulated by intracellular pathway activation and signaling from the surrounding microenvironment. It involves modulation of cell volume, cytoskeletal rearrangement, and isolation from compact extracellular matrix. In malignant brain tumors including high-grade gliomas, there are cells called brain tumor stem cells (BTSCs) with similar stem cell characteristics to NPCs but with uncontrolled cell proliferation and contribute to tumor initiation capacity, tumor progression, invasion, and tumor maintenance. These BTSCs are resistant to chemotherapy and radiotherapy, and their presence is believed to lead to tumor recurrence at distal sites from the original tumor location, principally due to their high migratory capacity. BTSCs are able to invade the brain parenchyma by utilizing many of the migratory mechanisms used by NPCs. However, they have an increased ability to infiltrate the tight brain parenchyma and utilize brain structures such as myelin tracts and blood vessels as migratory paths. In this article, we summarize recent findings on the mechanisms of cellular migration that overlap between NPCs and BTSCs. A better understanding of the intersection between NPCs and BTSCs will to provide a better comprehension of the BTSCs' invasive capacity and the molecular mechanisms that govern their migration and eventually lead to the development of new therapies to improve the prognosis of patients with malignant gliomas.

Glycine is able to induce both a motility speed in- and decrease during zebrafish neuronal migration

Various neurotransmitters influence neuronal migration in the developing zebrafish hindbrain. Migrating tegmental hindbrain nuclei neurons (THNs) are governed by depolarizing neurotransmitters (acetylcholine and glutamate), and glycine. In mature neurons, glycine binds to its receptor to hyperpolarize cells. This effect depends on the co-expression of the solute carrier KCC2. Immature precursors, however, typically express NKCC1 instead of KCC2, leading to membrane depolarization upon glycine receptor activation. As neuronal migration occurs in neurons after leaving the cell cycle and before terminal differentiation, we hypothesized that the switch from NKCC1 to KCC2 expression could alter the effect of glycine on THN migration. We tested this notion using in vivo cell tracking, overexpression of glycine receptor mutations and whole mount in situ hybridization. We summarize our findings in a speculative model, combining developmental age, glycine receptor strength and solute carrier expression to describe the effect of glycine on the migration of THNs.

Vitexin reduces epilepsy after hypoxic ischemia in the neonatal brain via inhibition of NKCC1

BACKGROUND

Neonatal hypoxic-ischemic brain damage, characterized by tissue loss and neurologic dysfunction, is a leading cause of mortality and a devastating disease of the central nervous system. We have previously shown that vitexin has been attributed various medicinal properties and has been demonstrated to have neuroprotective roles in neonatal brain injury models. In the present study, we continued to reinforce and validate the basic understanding of vitexin (45 mg/kg) as a potential treatment for epilepsy and explored its possible underlying mechanisms.

METHODS

P7 Sprague-Dawley (SD) rats that underwent right common carotid artery ligation and rat brain microvascular endothelial cells (RBMECs) were used for the assessment of Na⁺-K⁺-Cl^- co-transporter1 (NKCC1) expression, BBB permeability, cytokine expression, and neutrophil infiltration by western blot, q-PCR, flow cytometry (FCM), and immunofluorescence respectively. Furthermore, brain electrical activity in freely moving rats was recorded by electroencephalography (EEG).

RESULTS

Our data showed that NKCC1 expression was attenuated in vitexin-treated rats compared to the expression in the HI group in vivo. Oxygen glucose deprivation/reoxygenation (OGD) was performed on RBMECs to explore the role of NKCC1 and F-actin in cytoskeleton formation with confocal microscopy, N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide, and FCM. Concomitantly, treatment with vitexin effectively alleviated OGD-induced NKCC1 expression, which downregulated F-actin expression in RBMECs. In addition, vitexin significantly ameliorated BBB leakage and rescued the expression of tight junction-related protein ZO-1. Furthermore, inflammatory cytokine and neutrophil infiltration were concurrently and progressively downregulated with decreasing BBB permeability in rats. Vitexin also significantly suppressed brain electrical activity in neonatal rats.

CONCLUSIONS

Taken together, these results confirmed that vitexin effectively alleviates epilepsy susceptibility through inhibition of inflammation along with improved BBB integrity. Our study provides a strong rationale for the further development of vitexin as a promising therapeutic candidate treatment for epilepsy in the immature brain.

In vivo migration of endogenous brain progenitor cells guided by an injectable peptide amphiphile biomaterial

Biomaterials hold great promise in helping the adult brain regenerate and rebuild after trauma. Peptide amphiphiles (PAs) are highly versatile biomaterials, gelling and forming macromolecular structures when exposed to physiological levels of electrolytes. We are here reporting on the first ever in vivo use of self-assembling PA carrying a Tenascin-C signal (E₂ Ten-C PA) for the redirection of endogenous neuroblasts in the rodent brain. The PA forms highly aligned nanofibers, displaying the migratory sequence of Tenascin-C glycoprotein as epitope. In this in vivo work, we have formed in situ a gel of aligned PA nanofibers presenting a migratory Tenascin-C signal sequence in the ventral horn of the rostral migratory stream, creating a track reaching the neocortex. Seven days posttransplant, doublecortin positive cells were observed migrating inside and alongside the injected biomaterial, reaching the cortex. We observed a 24-fold increase in number of redirected neuroblasts for the E₂ Ten-C PA-injected animals compared to control. We also found injecting the E₂ Ten-C PA to cause minimal neuroinflammatory response. Analysing GFAP⁺ astrocytes and Iba1⁺ microglia activation, the PA does not elicit a stronger neuroinflammatory response than would be expected from a small needle stab wound. Redirecting endogenous neuroblasts and increasing the number of cells reaching a site of injury using PAs may open up new avenues for utilizing the pool of neuroblasts and neural stem cells within the adult brain for regenerating damaged brain tissue and replacing neurons lost to injury.

Brief Report: Robo1 Regulates the Migration of Human Subventricular Zone Neural Progenitor Cells During Development

Human neural progenitor cell (NPC) migration within the subventricular zone (SVZ) of the lateral ganglionic eminence is an active process throughout early brain development. The migration of human NPCs from the SVZ to the olfactory bulb during fetal stages resembles what occurs in adult rodents. As the human brain develops during infancy, this migratory stream is drastically reduced in cell number and becomes barely evident in adults. The mechanisms regulating human NPC migration are unknown. The Slit-Robo signaling pathway has been defined as a chemorepulsive cue involved in axon guidance and neuroblast migration in rodents. Slit and Robo proteins expressed in the rodent brain help guide neuroblast migration from the SVZ through the rostral migratory stream to the olfactory bulb. Here, we present the first study on the role that Slit and Robo proteins play in human-derived fetal neural progenitor cell migration (hfNPC). We describe that Robo1 and Robo2 isoforms are expressed in the human fetal SVZ. Furthermore, we demonstrate that Slit2 is able to induce a chemorepellent effect on the migration of hfNPCs derived from the human fetal SVZ. In addition, when Robo1 expression is inhibited, hfNPCs are unable to migrate to the olfactory bulb of mice when injected in the anterior SVZ. Our findings indicate that the migration of human NPCs from the SVZ is partially regulated by the Slit-Robo axis. This pathway could be regulated to direct the migration of NPCs in human endogenous neural cell therapy. Stem Cells 2017;35:1860-1865.

Bumetanide reduce the seizure susceptibility induced by pentylenetetrazol via inhibition of aberrant hippocampal neurogenesis in neonatal rats after hypoxia-ischemia

Hypoxia-ischemia brain damage (HIBD) is one of prevalent causes of neonatal mortality and morbidity. Our data demonstrated that hypoxia-ischemia (HI) induced Na⁺-K⁺-Cl^--co-transporter 1 (NKCC1) increasing in hippocampus. Previous studies demonstrated that NKCC1 regulates various stages of neurogenesis. In this study, we studied the role of increased NKCC1 in regulating of HI-induced neurogenesis. HIBD model was established in 7days old Sprague-Dawley rat pup, and the expression of NKCC1 was detected by western blot and qPCR. Brain electrical activity in freely rats was monitored by electroencephalography (EEG) recordings. HI-induced neurogenesis was detected by immunofluorescence staining. Neurobehavioral test was to investigate the neuro-protective role of bumetanide, an inhibitor of NKCC1, on neonatal rats after HI. The results showed that bumetanide treatment significantly reduced brain electrical activity and the seizure stage of epilepsy induced by pentylenetetrazol (PTZ) in vivo after HI. In addition, bumetanide restored aberrant hippocampal neurogenesis and associated cognitive function. Our data demonstrated that bumetanide reduces the susceptibility of epilepsy induced by PTZ in rats suffering from HI injury during neonatal period via restoring the ectopic newborn neurons in dentate gyrus (DG) and cognitive function.

Ion transporters in brain tumors

Ion transporters are important in regulation of ionic homeostasis, cell volume, and cellular signal transduction under physiological conditions. They have recently emerged as important players in cancer progression. In this review, we discussed two important ion transporter proteins, sodium-potassium-chloride cotransporter isoform 1 (NKCC-1) and sodium-hydrogen exchanger isoform 1 (NHE-1) in Glioblastoma multiforme (GBM) and other malignant tumors. NKCC-1 is a Na(+)- dependent Cl(-) transporter that mediates the movement of Na(+), K(+), and Cl(-) ions across the plasma membrane and maintains cell volume and intracellular K(+) and Cl(-) homeostasis. NHE-1 is a ubiquitously expressed cell membrane protein which regulates intracellular pH (pH(i)) and extracellular pH (pH(e)) homeostasis and cell volume. Here, we summarized recent pre-clinical experimental studies on NKCC-1 and NHE-1 in GBM and other malignant tumors, such as breast cancer, hepatocellular carcinoma, and lung cancer cells. These studies illustrated that pharmacological inhibition or down-regulation of these ion transporter proteins reduces proliferation, increases apoptosis, and suppresses migration and invasion of cancer cells. These new findings reveal the potentials of these ion transporters as new targets for cancer diagnosis and/or treatment.

NKCC1 mediates traumatic brain injury-induced hippocampal neurogenesis through CREB phosphorylation and HIF-1α expression

Traumatic brain injury (TBI) is one of the most prevalent causes of worldwide mortality and morbidity. We previously had evidenced that TBI induced Na-K-2Cl co-transporter (NKCC1) upregulation in hippocampus. Here, we aim to investigate the role of NKCC1 in TBI-induced neurogenesis and the detailed mechanisms. The TBI-associated alternations in the expression of NKCC1, HIF-1α, VEGF, MAPK cascade, and CREB phosphorylation were analyzed by Western blot. TBI-induced neurogenesis was determined by immuno-fluorescence labeling. Chromatin immunoprecipitation was used to elucidate whether HIF-1α would activate VEGF gene after TBI. We found that the level of hippocampal NKCC1 and VEGF began to rise 8 h after TBI, and both of them reached maxima at day 7. Along with the upregulation of NKCC1 and VEGF, MAPK cascade was activated and hippocampal neurogenesis was promoted. Administration of CREB antisense oligonucleotide significantly attenuated the expression of HIF-1α, while HIF-1α antisense oligonucleotide exhibited little effect on the expression of CREB. However, HIF-1α antisense oligonucleotide administration did effectively suppress the expression of VEGF. Our results of the chromosome immunoprecipitation also indicated that HIF-1α could directly act on the VEGF promoter and presumably would elevate the VEGF expression after TBI. All these results have illustrated the correlation between NKCC1 upregulation and TBI-associated neurogenesis. The pathway involves the activation of Raf/MEK/ERK cascade, CREB phosphorylation, and HIF-1α upregulation, and finally leads to the stimulation of VEGF expression and the induction of neurogenesis.

The Possible Roles of the Dentate Granule Cell's Leptin and Other Ciliary Receptors in Alzheimer's Neuropathology

Dentate-gyral granule cells in the hippocampus plus dentate gyrus memory-recording/retrieving machine, unlike most other neurons in the brain, are continuously being generated in the adult brain with the important task of separating overlapping patterns of data streaming in from the outside world via the entorhinal cortex. This "adult neurogenesis" is driven by tools in the mature granule cell's cilium. Here we report our discovery of leptin's LepRb receptor in this cilium. In addition, we discuss how ciliary LepRb signaling might be involved with ciliary p75NTR and SSTR3 receptors in adult neurogenesis and memory formation as well as attenuation of Alzheimer's neuropathology by reducing the production of its toxic amyloid-β-derived drivers.

Regulation of subventricular zone-derived cells migration in the adult brain

The subventricular zone of the lateral ventricles (SVZ) is the largest source of neural stem cells (NSCs) in the adult mammalian brain. Newly generated neuroblasts from the SVZ form cellular chains that migrate through the rostral migratory stream (RMS) into the olfactory bulb (OB), where they become mature neurons. Migration through the RMS is a highly regulated process of intrinsic and extrinsic factors, orchestrated to achieve direction and integration of neuroblasts into OB circuitry. These factors include internal cytoskeletal and volume regulators, extracellular matrix proteins, and chemoattractant and chemorepellent proteins. All these molecules direct the cells away from the SVZ, through the RMS, and into the OB guaranteeing their correct integration. Following brain injury, some neuroblasts escape the RMS and migrate into the lesion site to participate in regeneration, a phenomenon that is also observed with brain tumors. This review focuses on factors that regulate the migration of SVZ precursor cells in the healthy and pathologic brain. A better understanding of the factors that control the movement of newly generated cells may be crucial for improving the use of NSC-replacement therapy for specific neurological diseases.

PACAP modulation of calcium ion activity in developing granule cells of the neonatal mouse olfactory bulb

Ca(2+) activity in the CNS is critical for the establishment of developing neuronal circuitry prior to and during early sensory input. In developing olfactory bulb (OB), the neuromodulators that enhance network activity are largely unknown. Here we provide evidence that pituitary adenylate cyclase-activating peptide (PACAP)-specific PAC1 receptors (PAC1Rs) expressed in postnatal day (P)2-P5 mouse OB are functional and enhance network activity as measured by increases in calcium in genetically identified granule cells (GCs). We used confocal Ca(2+) imaging of OB slices from Dlx2-tdTomato mice to visualize GABAergic GCs. To address whether the PACAP-induced Ca(2+) oscillations were direct or indirect effects of PAC1R activation, we used antagonists for the GABA receptors (GABARs) and/or glutamate receptors (GluRs) in the presence and absence of PACAP. Combined block of GABARs and GluRs yielded a 66% decrease in the numbers of PACAP-responsive cells, suggesting that 34% of OB neurons are directly activated by PACAP. Similarly, immunocytochemistry using anti-PAC1 antibody showed that 34% of OB neurons express PAC1R. Blocking either GluRs or GABARs alone indirectly showed that PACAP stimulates release of both glutamate and GABA, which activate GCs. The appearance of PACAP-induced Ca(2+) activity in immature GCs suggests a role for PACAP in GC maturation. To conclude, we find that PACAP has both direct and indirect effects on neonatal OB GABAergic cells and may enhance network activity by promoting glutamate and GABA release. Furthermore, the numbers of PACAP-responsive GCs significantly increased between P2 and P5, suggesting that PACAP-induced Ca(2+) activity contributes to neonatal OB development.

The GABA excitatory/inhibitory developmental sequence: a personal journey

The developing brain is talkative but its language is not that of the adult. Most if not all voltage and transmitter-gated ionic currents follow a developmental sequence and network-driven patterns differ in immature and adult brains. This is best illustrated in studies engaged almost three decades ago in which we observed elevated intracellular chloride (Cl(-))i levels and excitatory GABA early during development and a perinatal excitatory/inhibitory shift. This sequence is observed in a wide range of brain structures and animal species suggesting that it has been conserved throughout evolution. It is mediated primarily by a developmentally regulated expression of the NKCC1 and KCC2 chloride importer and exporter respectively. The GABAergic depolarization acts in synergy with N-methyl-d-aspartate (NMDA) receptor-mediated and voltage-gated calcium currents to enhance intracellular calcium exerting trophic effects on neuritic growth, migration and synapse formation. These sequences can be deviated in utero by genetic or environmental insults leading to a persistence of immature features in the adult brain. This "neuroarcheology" concept paves the way to novel therapeutic perspectives based on the use of drugs that block immature but not adult currents. This is illustrated notably with the return to immature high levels of chloride and excitatory actions of GABA observed in many pathological conditions. This is due to the fact that in the immature brain a down regulation of KCC2 and an up regulation of NKCC1 are seen. Here, I present a personal history of how an unexpected observation led to novel concepts in developmental neurobiology and putative treatments of autism and other developmental disorders. Being a personal account, this review is neither exhaustive nor provides an update of this topic with all the studies that have contributed to this evolution. We all rely on previous inventors to allow science to advance. Here, I present a personal summary of this topic primarily to illustrate why we often fail to comprehend the implications of our own observations. They remind us - and policy deciders - why Science cannot be programed, requiring time, and risky investigations that raise interesting questions before being translated from bench to bed. Discoveries are always on sideways, never on highways.

Regulation of adult neurogenesis by GABAergic transmission: signaling beyond GABAA-receptors

In the adult mammalian brain, neurogenesis occurs in the olfactory bulb (OB) and in the dentate gyrus (DG) of the hippocampus. Several studies have shown that multiple stages of neurogenesis are regulated by GABAergic transmission with precise spatio-temporal selectivity, and involving mechanisms common to both systems or specific only to one. In the subgranular zone (SGZ) of the DG, GABA neurotransmitter, released by a specific population of interneurons, regulates stem cell quiescence and neuronal cell fate decisions. Similarly, in the subventricular zone (SVZ), OB neuroblast production is modulated by ambient GABA. Ambient GABA, acting on extrasynaptic GABAA receptors (GABAAR), is also crucial for proper adult-born granule cell (GC) maturation and synaptic integration in the OB as well as in the DG. Throughout adult-born neuron development, various GABA receptors and receptor subunits play specific roles. Previous work has demonstrated that adult-born GCs in both the OB and the DG show a time window of increased plasticity in which adult-born cells are more prone to modification by external stimuli. One mechanism that controls this "critical period" is GABAergic modulation. Indeed, depleting the main phasic GABAergic inputs in adult-born neurons results in dramatic effects, such as reduction of spine density and dendritic branching in adult-born OB GCs. In this review, we systematically compare the role of GABAergic transmission in the regulation of adult neurogenesis between the OB and the hippocampus, focusing on the role of GABA in modulating plasticity and critical periods of adult-born neuron development. Finally, we discuss signaling pathways that might mediate some of the deficits observed upon targeted deletion of postsynaptic GABAARs in adult-born neurons.

GABAergic striatal neurons project dendrites and axons into the postnatal subventricular zone leading to calcium activity

GABA regulates the behavior of neuroblasts and neural progenitor cells in the postnatal neurogenic subventricular zone (SVZ) through GABAA receptor (GABAAR)-mediated calcium increases. However, the source of GABA necessary for sufficient GABAAR-mediated depolarization and calcium increase has remained speculative. Here, we explored whether GABAergic striatal neurons functionally connect with SVZ cells. Using patch clamp recordings or single cell electroporation, striatal neurons along the SVZ were filled with a fluorescent dye revealing that they send both dendrites and axons into the SVZ. About 93% of the recorded neurons were medium spiny or aspiny GABAergic neurons and each neuron sent 3-4 processes into the SVZ covering ~56 μm. Using calcium imaging, we found that depolarization of striatal neurons led to increased calcium activity in SVZ cells that were mediated by GABAAR activation. Collectively, these findings undercover a novel mode of signaling in the SVZ providing a mechanism of brain activity-mediated regulation of postnatal neurogenesis through GABAergic striatal activity.

Direct control of Na(+)-K(+)-2Cl(-)-cotransport protein (NKCC1) expression with aldosterone

Sodium/potassium/chloride cotransporter (NKCC1) proteins play important roles in Na(+) and K(+) concentrations in key physiological systems, including cardiac, vascular, renal, nervous, and sensory systems. NKCC1 levels and functionality are altered in certain disease states, and tend to decline with age. A sensitive, effective way of regulating NKCC1 protein expression has significant biotherapeutic possibilities. The purpose of the present investigation was to determine if the naturally occurring hormone aldosterone (ALD) could regulate NKCC1 protein expression. Application of ALD to a human cell line (HT-29) revealed that ALD can regulate NKCC1 protein expression, quite sensitively and rapidly, independent of mRNA expression changes. Utilization of a specific inhibitor of mineralocorticoid receptors, eplerenone, implicated these receptors as part of the ALD mechanism of action. Further experiments with cycloheximide (protein synthesis inhibitor) and MG132 (proteasome inhibitor) revealed that ALD can upregulate NKCC1 by increasing protein stability, i.e., reducing ubiquitination of NKCC1. Having a procedure for controlling NKCC1 protein expression opens the doors for therapeutic interventions for diseases involving the mis-regulation or depletion of NKCC1 proteins, for example during aging.

Functional circuits of new neurons in the dentate gyrus

The hippocampus is crucial for memory formation. New neurons are added throughout life to the hippocampal dentate gyrus (DG), a brain area considered important for differential storage of similar experiences and contexts. To better understand the functional contribution of adult neurogenesis to pattern separation processes, we recently used a novel synapse specific trans-neuronal tracing approach to identify the (sub) cortical inputs to new dentate granule cells (GCs). It was observed that newly born neurons receive sequential innervation from structures important for memory function. Initially, septal-hippocampal cells provide input to new neurons, including transient innervation from mature GCs as well as direct feedback from area CA3 pyramidal neurons. After about 1 month perirhinal (PRH) and lateral entorhinal cortex (LEC), brain areas deemed relevant to integration of novel sensory and environmental information, become substantial input to new GCs. Here, we review the developmental time-course and proposed functional relevance of new neurons, within the context of their unique neural circuitry.

Both NKCC1 and anion exchangers contribute to Cl⁻ accumulation in postnatal forebrain neuronal progenitors

Neuronal progenitors are continuously generated in the postnatal rodent subventricular zone and migrate along the rostral migratory stream to supply interneurons in the olfactory bulb. Nonsynaptic GABAergic signaling affects the postnatal neurogenesis by depolarizing neuronal progenitors, which depends on an elevated intracellular Cl(-) concentration. However, the molecular mechanism responsible for Cl(-) accumulation in these cells still remains elusive. Using confocal Ca(2+) imaging, we found that GABA depolarization-induced Ca(2+) increase was either abolished by bumetanide, a specific inhibitor of the Na(+) -K(+) -2Cl(-) cotransporter, or reduced by partial replacement of extracellular Na(+) with Li(+) , in the HEPES buffer but not in the CO(2)/HCO₃⁻ buffer. GABA depolarization-induced Ca(2+) increase in CO(2)/HCO₃⁻ buffer was abolished by a combination of bumetanide with the anion exchanger inhibitor DIDS or with the carbonic anhydrase inhibitor acetozalimide. Using gramicidin-perforated patch-clamp recording, we further confirmed that bumetanide, together with DIDS or acetozalimide, reduced the intracellular chloride concentration in the neuronal progenitors. In addition, with BrdU labeling, we demonstrated that blocking of the Na(+) -K(+) -2Cl(-) cotransporter, but not anion exchangers, reduced the proliferation of neuronal progenitors. Our results indicate that both the Na(+) -K(+) -2Cl(-) cotransporter and anion exchangers contribute to the elevated intracellular chloride responsible for the depolarizing action of GABA in the postnatal forebrain neuronal progenitors. However, the Na(+) -K(+) -2Cl(-) cotransporter displays an additional effect on neuronal progenitor proliferation.

Neural stem cells: mechanisms and modeling

In the adult brain, neural stem cells have been found in two major niches: the dentate gyrus and the subventricular zone [corrected]. Neurons derived from these stem cells contribute to learning, memory, and the autonomous repair of the brain under pathological conditions. Hence, the physiology of adult neural stem cells has become a significant component of research on synaptic plasticity and neuronal disorders. In addition, the recently developed induced pluripotent stem cell technique provides a powerful tool for researchers engaged in the pathological and pharmacological study of neuronal disorders. In this review, we briefly summarize the research progress in neural stem cells in the adult brain and in the neuropathological application of the induced pluripotent stem cell technique.

Cell-autonomous and cell-to-cell signalling events in normal and altered neuronal migration

The cerebral cortex is a complex six-layered structure that contains an important diversity of neurons, and has rich local and extrinsic connectivity. Among the mechanisms governing the cerebral cortex construction, neuronal migration is perhaps the most crucial as it ensures the timely formation of specific and selective neuronal circuits. Here, we review the main extrinsic and extrinsic factors involved in regulating neuronal migration in the cortex and describe some environmental factors interfering with their actions.

Activity-induced remodeling of olfactory bulb microcircuits revealed by monosynaptic tracing

The continued addition of new neurons to mature olfactory circuits represents a remarkable mode of cellular and structural brain plasticity. However, the anatomical configuration of newly established circuits, the types and numbers of neurons that form new synaptic connections, and the effect of sensory experience on synaptic connectivity in the olfactory bulb remain poorly understood. Using in vivo electroporation and monosynaptic tracing, we show that postnatal-born granule cells form synaptic connections with centrifugal inputs and mitral/tufted cells in the mouse olfactory bulb. In addition, newly born granule cells receive extensive input from local inhibitory short axon cells, a poorly understood cell population. The connectivity of short axon cells shows clustered organization, and their synaptic input onto newborn granule cells dramatically and selectively expands with odor stimulation. Our findings suggest that sensory experience promotes the synaptic integration of new neurons into cell type-specific olfactory circuits.

Identification of key residues involved in the dimerization of the secretory Na(+)-K(+)-2Cl(-) cotransporter NKCC1

The "secretory" Na(+)-K(+)-2Cl(-) cotransporter, NKCC1, belongs to the SLC12 gene family of electroneutral cation-chloride cotransporters. A number of these proteins, including NKCC1 itself, exist as homodimers in the membrane, suggesting that this may be a common feature of the SLC12 family. We have previously demonstrated that replacing the C-terminus of NKCC1 with that of its close homologue NKCC2 produced a fully functional chimeric protein that formed homodimers but did not dimerize with NKCC1. Here we employ a novel co-immunoprecipitation assay to study the dimerization interaction of NKCC1 using additional NKCC1/NKCC2 C-terminal chimeras and point mutants. Our results indicate that the substitution of a number of regions of the C-terminus of NKCC1 with the corresponding sequence from NKCC2 results in weakened dimerization with wild-type NKCC1, demonstrating that various residues play a role in this interaction. Most interestingly, however, we find that the replacement of a single NKCC1 residue, G812, with cysteine, the corresponding amino acid in NKCC2, results in a point mutant that displays no significant dimerization with the wild-type protein. In addition to this effect on heterodimer formation, we also find that G812 mutants can nevertheless form homodimers but that this interaction can be weaker than that observed for wild-type NKCC1. We demonstrate that our results are consistent with at least one established mechanism of protein dimer formation, that of "domain swapping", as well as with a recently reported crystal structure of the C-terminus of a bacterial SLC12 homologue.

Abnormal neuronal migration changes the fate of developing neurons in the postnatal olfactory bulb

Neuronal precursors are continuously integrated into the adult olfactory bulb (OB). The vast majority of these precursor cells originates from the subventricular zone and migrates along the rostral migratory stream (RMS) en route to the OB. This process, called postnatal neurogenesis, results from intricate pathways depending both on cell-autonomous factors and extrinsic regulation provided by the local environment. Using electroporation in postnatal mice to label neuronal precursors with green fluorescent protein (GFP) and to reduce the expression levels of doublecortin (DCX) with short-hairpin (Sh) RNA, we investigated the consequences of impairing migration on the fate of postnatal-formed neurons. First, we showed that electroporation of Dcx ShRNA plasmid efficiently knocks down the expression of DCX and disrupts cells migration along the RMS. Second, we found misplaced anomalous migrating cells that displayed defects in polarity and directionality. Third, patch-clamp recordings performed at 5-7 days post-electroporation (dpe) revealed increased density of voltage-dependent Na(+) channels and enhanced responsiveness to GABA(A) receptor agonist. At later time points (i.e., 12 and 30 dpe), most of the Dcx ShRNA(+) cells developed in the core of the OB and displayed aberrant dendritic length and branching. Additional analysis revealed the formation of GABAergic and glutamatergic synaptic inputs on the mispositioned neurons. Finally, quantifying fate determination by numbering the proportion of GFP(+)/calretinin(+) newborn neurons revealed that Dcx ShRNA(+) cells acquire mature phenotype despite their immature location. We conclude that altering the pace of migration at early stages of postnatal neurogenesis profoundly modifies the tightly orchestrated steps of neuronal maturation, and unveils the influence of microenvironment on controlling neuronal development in the postnatal forebrain.

From progenitors to integrated neurons: role of neurotransmitters in adult olfactory neurogenesis

Adult neurogenesis is due to the persistence of pools of constitutive stem cells able to give rise to a progeny of proliferating progenitors. In rodents, adult neurogenic niches have been found in the subventricular zone (SVZ) along the lateral ventricles and in the subgranular zone of the dentate gyrus in the hippocampus. SVZ progenitors undergo a unique process of tangential migration from the lateral ventricle to the olfactory bulb (OB) where they differentiate mainly into GABAergic interneurons in the granule and glomerular layers. SVZ progenitor proliferation, migration and differentiation into fully integrated neurons, are strictly related processes regulated by complex interactions between cell intrinsic and extrinsic influences. Numerous observations demonstrate that neurotrasmitters are involved in all steps of the adult neurogenic process, but the understanding of their role is hampered by their intricate mechanism of action and by the highly complex network in which neurotransmitters work. By considering the three main steps of olfactory adult neurogenesis (proliferation, migration and integration), this review will discuss recent advances in the study of neurotransmitters, highlighting the regulatory mechanisms upstream and downstream their action.

Ion channels and transporters [corrected] in cancer. 2. Ion channels and the control of cancer cell migration

A hallmark of high-grade cancers is the ability of malignant cells to invade unaffected tissue and spread disease. This is particularly apparent in gliomas, the most common and lethal type of primary brain cancer affecting adults. Migrating cells encounter restricted spaces and appear able to adjust their shape to accommodate to narrow extracellular spaces. A growing body of work suggests that cell migration/invasion is facilitated by ion channels and transporters. The emerging concept is that K(+) and Cl(-) function as osmotically active ions, which cross the plasma membrane in concert with obligated water thereby adjusting a cell's shape and volume. In glioma cells Na(+)-K(+)-Cl(-) cotransporters (NKCC1) actively accumulate K(+) and Cl(-), establishing a gradient for KCl efflux. Ca(2+)-activated K(+) channels and voltage-gated Cl(-) channels are largely responsible for effluxing KCl promoting hydrodynamic volume changes. In other cancers, different K(+) or even Na(+) channels may function in concert with a variety of Cl(-) channels to support similar volume changes. Channels involved in migration are frequently regulated by Ca(2+) signaling, most likely coupling extracellular stimuli to cell migration. Importantly, the inhibition of ion channels and transporters appears to be clinically relevant for the treatment of cancer. Recent preclinical data indicates that inhibition of NKCC1 with an FDA-approved drug decreases neoplastic migration. Additionally, ongoing clinical trials demonstrate that an inhibitor of chloride channels may be a therapy for the treatment of gliomas. Data reviewed here strongly indicate that ion channels are a promising target for the development of novel therapeutics to combat cancer.